Fix bug in king attacking detection

A bug was introduced allowing kings to attack more than one square away

README.md

@@ -1,7 +1,6 @@
 # A chess game & engine
 
 ## Features
-- 
 - Computer move generation
  - minimax (negamax), alpha-beta pruning & iterative deepening
  - Multithreaded search (Lazy SMP) on platforms supporting C11 threads

src/engine.c

@@ -990,8 +990,8 @@ bool is_piece_attacked(struct GameState *state, struct BoardPos attackee_pos, en
  const struct BoardPos translation = PIECE_MOVE_DIRECTIONS[Queen - 1][i];
 
  const bool is_diagonal = abs(translation.file) == abs(translation.rank);
- const bool is_king = abs(translation.file) <= 1 && abs(translation.rank) <= 1;
-
+ bool is_king = true;
+ 
  struct BoardPos check = boardpos_add(attackee_pos, translation);
  while (!boardpos_eq(check, NULL_BOARDPOS)) {
  struct Piece check_piece = get_piece(state, check);
@@ -1011,6 +1011,9 @@ bool is_piece_attacked(struct GameState *state, struct BoardPos attackee_pos, en
  }
  }
 
+ // Kings can only move one square.
+ is_king = false;
+
  // Queens, rooks and bishops can attack over multiple squares in the same direction, so the
  // check continues for every square in that direction. Overflow is handled by boardpos_add,
  // NULL_BOARDPOS will be returned if the add overflows.